I have a 54 liter (14 US gallon) community tank with 6 neon tetras and 5 guppies. It's heated at 24 Celsius and is filtered by an UGF (under-gravel filter).
The problem is the neon tetras keep getting ragged/torn fins but I don't think it's fin rot as there is no discoloration at all and after a week or so the fins grow back. I'm pretty sure there are no sharp decorations and all fish are active, healthy (apart from the fins) and eating well. The water parameters are all except-able however I cannot measure ammonia but I don't think this is a problem as the guppies would get red gills if the levels of ammonia were too high. I feed the fish on Tropical Fish flakes and occasionally blood worms. I do a water change once a week (25% ish). They've had split fins on-and-off for the whole time I've had the tank (6 months).

The thing is, although the split/ragged fins on the neon tetras don't seem to be a problem, I don't think it does them any good, so how can I stop them from getting ragged/split fins? Also, could it be a disease of some kind and if so how can I treat it?

If you've had the tank for 6 months it's most likely cycled, but you really should have a test for ammonia. Once the fish show signs of stress from ammonia, the damage has already been done. Neons aren't the hardiest of fish.

Neon tetra are a schooling fish. Six fish is the minimum grouping they should be kept in because they commonly fight within themselves. More fish means the aggression is more spread out. It sounds like you have some infighting. You could try introducing another 3-4 neons and see if they calm down a little bit.

The other possibility is that the neons are stressed, and this stress is leading to torn fins. The temp is good for them, but the water might be too hard; they might not have enough cover. Either way the stress leads to a weakened fish and that shows through in the torn fins.

I have two swords, a plastic cave that I sanded down and need to put some boiled driftwood back in. I am soon going to do a "make over" by adding lots more plants etc. Please note I do know now that the swords shouldn't be in a tank with an UGF and I will soon remove them.

I could possibly add a few more neon tetras after I've done the "make over". I have another question, I am going to replace the UGF with an internal filter, do I need to run the internal filter for several weeks/months before I take out the UGF so that the filter is cycled and the bacteria lost on the UGF is replaced by the bacteria on the internal filter? I am replacing the filter so that I can have rooted plants.

When you remove the swords, get some other plants like anubias or java fern. Neons are a little more sensitive than most people think and do best with plants around. Stuffing that tank with as many plants as possible is going to make your neons feel much more comfortable.

The aim of the UGF is to have a good colony of bacteria in the substrate by pulling water and oxygen through the substrate. I would run the internal filter for a few weeks before removing the UGF just to make sure it's well-seeded.

Ok thanks. When I do the "make over" I was basically going to add more plants any way and I was thinking of adding anubais, java fern and moss and maybe some elodea. Now I'll run the filter for a few weeks but first I need to add some aquarium sponge to the intake to make it less powerful.

How about more water changes? I am working in the office where they have 45 gall and someone who is coming to clean the tank does like 50-60% water out on regular basis and looks like fish doing great for long time.

How about more water changes? I am working in the office where they have 45 gall and someone who is coming to clean the tank does like 50-60% water out on regular basis and looks like fish doing great for long time.

I was thinking about increasing the percentage of the water I change every week. Thanks for the advice.

I also know that UGFs are famous for sucking fish in and under. There's a possibility your neons are getting caught in the filter too. That aside, I also agree with koimaiden, that there's some infighting going on.

I also know that UGFs are famous for sucking fish in and under. There's a possibility your neons are getting caught in the filter too. That aside, I also agree with koimaiden, that there's some infighting going on.

That's interesting, I'd never thought of that, although I've never seen them being sucked in......